But a California woman is suing the fast food chain for false advertising, claiming its beefy filling is only 35 percent ground beef.

"We are asking that they stop saying that they are selling beef," a representative from the California law firm Beasley, Allen, Crow, Methvin, Portis & Miles, which is representing the woman in a class action, told the New York Daily News.

According to the U.S. Department of Agriculture, "Ground beef can have seasonings, but no water, phosphates, extenders or binders added." The lawsuit, filed Jan. 19 in a California federal court, claims Taco Bell's "seasoned ground beef" is two-thirds binders, extenders, preservatives, additives and other agents. The lawsuit wants Taco Bell to publicly come clean about the content of its Mexican-inspired products.

But for 99 cents -- and ready in seconds -- who expects Grade A beef?

"It may be unrealistic to think that you're going to get a high-quality meat product at an inexpensive fast-food joint," said Lisa Cimperman, a registered dietitian at University Hospitals Case Medical Center in Cleveland. "Ground beef is an expensive ingredient, so it's probably one place they're going to cut corners."

"In most cases, these additives are not necessarily harmful," said Cimperman. "They're added for shelf stability, texture and flavor."

Nevertheless, the plaintiff's "beef" is legitimate, Cimperman said. But she hesitates to say the lawsuit will dissuade Taco Bell devotees.

"People who are interested in eating organic, grass-fed beef aren't eating at Taco Bell," Cimperman said. "I think that if you choose to eat there, it's a conscious decision to eat something less healthy."

Like many fast-food chains, Taco Bell caters to its clientele in three ways: Convenience, taste and price, according to Sara Bleich, assistant professor at the Johns Hopkins Bloomberg School of Public Health in Baltimore. But there is a growing push from consumers, policymakers and even fast-food chain corporate decision makers to become more transparent about nutrition and promote healthy alternatives.

"It's partly fueled by public demand, and partly by the government's requiring fast-food restaurants to post nutritional information," Bleich said. "But the fast-food industry has also taken it upon itself to provide a healthier set of options, and I view that as a positive thing."

Good Value, Bad Food?

But value menus that encourage the overconsumption of low-nutrition foods are still a big problem. At Taco Bell, an extra dollar gets you a bag of Doritos and a soda with your beefy five-layer burrito.

"This is a very good example of food low in nutritional value and high in calories that's also inexpensive," Cimperman said. "You see a greater incidence of obesity in areas of lower socioeconomic status, and I really do think this is part of the problem. These 'value' menus appeal to people who want the highest quantity for the least amount of money."

Although fast-food chains contribute to the obesity problem, Bleich believes they could also become part of the solution.

"They need to create more healthy options and advertise them more -- especially in poor or minority areas," Bleich said.

Changing the default is another way to promote healthier options, Bleich said. Making people opt for a baked potato over fries might make them think twice about what they're eating, she said.